LipidsEdexcel A-Level Biology B: Flashcards
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Question
What is a triglyceride made from?
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- What is a triglyceride made from?
- One glycerol molecule and three fatty acids.
- Which bond joins a fatty acid to glycerol?
- An ester bond, formed in a condensation reaction.
- How many water molecules are released when one triglyceride forms?
- Three, one for each ester bond.
- What is a saturated fatty acid?
- One with no C=C double bonds in its hydrocarbon tail.
- What is an unsaturated fatty acid?
- One with at least one C=C double bond in its hydrocarbon tail.
- Why are unsaturated fats usually liquid at room temperature?
- Double bonds kink the chains so molecules cannot pack closely, giving fewer intermolecular forces.
- Why are triglycerides a good energy store?
- They have many C–H bonds, releasing more energy per gram than carbohydrate, and are insoluble.
- How do triglycerides waterproof?
- Their hydrocarbon tails are hydrophobic and repel water.
- How does a layer of fat insulate an animal?
- Fat is a poor conductor of heat, so it reduces heat loss.
- How does a phospholipid differ from a triglyceride?
- One fatty acid is replaced by a phosphate group.
- Which part of a phospholipid is hydrophilic?
- The phosphate head.
- Why do phospholipids form a bilayer in water?
- Heads face the water and hydrophobic tails face inwards, away from water.
- Which substances can cross the phospholipid bilayer easily?
- Small non-polar molecules such as oxygen and carbon dioxide.
Exam questions on Lipids
- A food technologist is comparing two cooking fats. Butter is solid at room temperature and contains mostly saturated fatty acids, whereas olive oil is liquid at room temperature and contains mostly unsaturated fatty acids.Explain why olive oil is liquid at room temperature but butter is solid.2 marks
- A camel stores fat in its hump, which it can use as an energy reserve in the desert. A seal living in cold Arctic water has a thick layer of fat, called blubber, under its skin.Explain how the blubber helps the seal to survive in cold water.2 marks
- A student uses a model kit to build a triglyceride. The model contains one glycerol molecule and three fatty acid molecules. Two of the fatty acids each contain one C=C double bond in the hydrocarbon chain and the third has no C=C double bonds.Describe how the glycerol and fatty acids in the model are joined to form a triglyceride.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).